cider-test: don't render a newline between expected and actual

CHANGELOG.md

@@ -26,6 +26,7 @@
 - Bump the injected `cider-nrepl` to [0.34](https://github.com/clojure-emacs/cider-nrepl/blob/v0.34.0/CHANGELOG.md#0340-2023-08-03).
 - Improve `nrepl-dict` error reporting.
 - Preserve the `:cljs-repl-type` more reliably.
+- [#3375](https://github.com/clojure-emacs/cider/pull/3375): `cider-test`: don't render a newline between expected and actual, most times. 
 
 ## 1.7.0 (2023-03-23)
 

cider-test.el

@@ -400,6 +400,12 @@ With the actual value, the outermost '(not ...)' s-expression is removed."
         (cider-insert "t" 'font-lock-constant-face t))
       (insert "\n\n"))))
 
+(defun cider-test--string-contains-newline (input-string)
+  "Returns whether INPUT-STRING contains an escaped newline."
+  (when (stringp input-string)
+    (and (string-match-p "\\n" input-string)
+         t)))
+
 (defun cider-test-render-assertion (buffer test)
   "Emit into BUFFER report detail for the TEST assertion."
   (with-current-buffer buffer
@@ -427,12 +433,17 @@ With the actual value, the outermost '(not ...)' s-expression is removed."
             (when expected
               (insert-label "expected")
               (insert-rect expected)
-              (insert "\n"))
+              ;; Only place a newline between expected and actual when the values are deemed 'dense',
+              ;; otherwise favor compact output:
+              (when (or (cider-test--string-contains-newline expected)
+                        (cider-test--string-contains-newline actual))
+                (insert "\n")))
             (if diffs
                 (dolist (d diffs)
                   (cl-destructuring-bind (actual (removed added)) d
                     (insert-label "actual")
                     (insert-rect actual)
+                    (insert "\n")
                     (insert-label "diff")
                     (insert "- ")
                     (insert-rect removed)

test/cider-test-tests.el

@@ -0,0 +1,37 @@
+;;; cider-test-tests.el  -*- lexical-binding: t; -*-
+
+;; Copyright © 2023 Bozhidar Batsov
+
+;; Author: Bozhidar Batsov <[email protected]>
+
+;; This file is NOT part of GNU Emacs.
+
+;; This program is free software: you can redistribute it and/or
+;; modify it under the terms of the GNU General Public License as
+;; published by the Free Software Foundation, either version 3 of the
+;; License, or (at your option) any later version.
+;;
+;; This program is distributed in the hope that it will be useful, but
+;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;; General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see `http://www.gnu.org/licenses/'.
+
+;;; Commentary:
+
+;; This file is part of CIDER
+
+;;; Code:
+
+(require 'buttercup)
+(require 'cider-test)
+
+(describe "cider-test--string-contains-newline"
+  (expect (cider-test--string-contains-newline "Hello\nWorld")
+          :to-equal
+          nil)
+  (expect (cider-test--string-contains-newline "Hello\\nWorld")
+          :to-equal
+          t))